Process for recovering carbon monoxide from fuel gas

ABSTRACT

Carbon monoxide is recovered from a fuel gas by compressing a fuel gas containing carbon monoxide and by reacting the carbon monoxide with a lower alkyl alcohol to form alkyl formate. The formate is separated from the fuel gas, and the carbon monoxide is regenerated by decomposition of the formate.

United States Patent 1191 Lynn et al.

[541 PROCESS FOR RECOVERING CARBON MONOXIDE FROM FUEL GAS [451 Feb. 13,1973 2,849,082 8/1958 Giammarco ..23/2 R 2,519,284 8/1950 Ray et al..23/2 R [75] Inventors: James B. Lynn, Bethlehem; Alan H.

Singleton, Emmaus, both of Pa. Primary ExaminerOscar R. Vertiz [73]Assignee: Bethlehem Steel Corporation Ass'smm ExammerHoke MmerAtt0rneyJoseph J. OKeeffe [22] Filed: March 19, 1971 [21] Appl. No.:125,974 ABSTRACT 52 11.5. C1 ..423/247 260/532 is 'ewvered mm a fuel gasby 51 Int. Cl ..C0lb 31/1s,c(i7 69/06 mpressmg fuel gas Naming carbonmmoxide 5 Field of 23 204 My 2 R, 2 2 0 4495 and by reacting the carbonmonoxide with a lower 26Q/532478;423/247 alkyl alcohol to form alkylfol-mate. The formate is separated from the fuel gas, and the carbonmonoxide [56] References Cited is regenerated by decomposition of theformate.

UNITED STATES PATENTS 6 Claims, 2 Drawing Figures 2,l l7,600 5/1938Brill et al 260/532 FUEL 6A5 CHRBON MONOX/OE' COMPRESSOR l/E/VT l3COOLER 1/ EN 7' C ONDE USER E 0 /.9 A flcr R COOLEE 22 ll /4 a DEGHSSERC 0 aavsm me 26 PATENTEB FEB 1 3197s FUEL H6. C/mamv MO/VOX/DECOMPRESSOR VENT V l, c001. ER

VENT CONDENSER Z8 30 REACT COOL a? /9 /2 jlg 39 05645554? 6 r38 aavfimme2e flRBO/V Molvox/os 48 2 45 C001. ER

CONDEMSER 46 FUEZ C 0 50 Guam-roe COMPRESSOR 44 l0 v ,w' 42 E KEIKTOKVZQZOL5Q INVENTORS James 5. L nn Wig, b J/h /efM ATTORNEY PROCESS FORRECOVERING CARBON MONOXIDE FROM FUEL GAS BACKGROUND OF THE INVENTIONThis invention relates to gas separation, and more particularly to therecovery of carbon monoxide from fuel gas.

Carbon monoxide is a common constituent of fuel gases, such as forexample, synthesis gas, water gas, steam-hydrocarbon reforming gases,blast furnace gas, etc. Removing and recovering carbon monoxide fromfuel gas, either as a step in purifying the fuel gas or, to provide asource of carbon monoxide as a raw material, is well known in the art.However, prior art processes have been generally directed toabsorption/desorption processes in which carbon monoxide is absorbedinto a solution, usually cuprous chloride or cuprous ammonium solutions,and thus separated from the fuel gas, with which is it associated.Recovery, if desired, is then by desorption.

These prior art methods of carbon monoxide separation and recovery havemany disadvantages associated with their use. Absorption/desorptionprocesses are multi-step processes involving expensive equipment andmaterials. Further, prior art carbon monoxide recovery methods have notreadily produced carbon monoxide of high purity.

SUMMARY OF THE INVENTION This invention discloses a method of recoveringcarbon monoxide from a fuel gas with which it is associated whichobviates the aforementioned prior art problems. A fuel gas containingcarbon monoxide is first compressed and then the carbon monoxide presentin the fuel gas is reacted with an alkyl alcohol such as methanol in thepresence of a corresponding alkali metal alkoxide such as sodiummethoxide to form an alkyl formate. The alkyl formate in alcoholsolution is fluid, thus easily separated from the residual fuel gas by,for example, venting the fuel gas. Carbon monoxide is regenerated bydecomposing the alkyl formate to recover the carbon monoxide and thealcohol. The latter is recycled and reused.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow diagram of thisinvention. FIG. 2 is a flow diagram of an alternate embodiment of thisinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a fuel gascomprising approximately in molar per cent, 55 percent nitrogen, 25percent carbon monoxide, 4.5 percent hydrogen and 0.5 percent methane,and from which carbon dioxide and water have been previously removed,enters compressor where it is compressed to a pressure between about2500 to 5000 psig (the partial pressure of carbon monoxide present isfrom about 625 to about 1250 psig). From compressor 10 the fuel gasenters reactor 12 by line 11. Reactor 12 contains, in addition to theentering fuel gas, sodium methoxide (NaO CH dissolved in methanol (CHOH) in the ratio of about 1 part by weight sodium methoxide per 100parts methanol. The temperature in reactor 12 is maintained at about 60to 100 C. to synthesize methyl formate by carbon monoxideesterification. During esterificatio n, the fuel gas residue iscontinuously vented through line 13. Methyl formate in a methanolsolution leaves reactor 12 by line 14 and enters cooler 16 where thetemperature is lowered to about 15 to 20 C. and proceeds from therethrough pressure reducing metering valve 17 to degasser 18. In degasser18, the methyl formatemethanol solution pressure is lowered to causedegassing of dissolved contaminant gases. The fuel gas residue thusreleased is vented from degasser 18 by line 19. The methylformate-methanol solution leaves degasser 18 by line 20 and proceedsthrough pump 22 to carbon monoxide generator 26. In carbon monoxidegenerator 26, the methyl formate-methanol solution is heated to fromabout 35 C. to about 200 C. to cause the methyl formate ester todecompose, regenerating carbon monoxide and methyl alcohol. The pressurein carbon monoxide generator 26 is preferably maintained the same as indegasser l8. Gaseous products in carbon monoxide generator 26, whichinclude carbon monoxide, methyl formate vapor and methanol vapor, leavecarbon monoxide generator 26 by line 28 to cooler/condenser 30. Liquidmethanol leaves carbon monoxide generator 26 by line 38 and is recycledby pump 34 to reactor 12.

i In cooler/condenser 30 the gases entering through line 28 are cooledto purify, by condensation of the methanol and methyl formate, thecarbon monoxide which emerges from cooler/condenser 30 at line 36.Methanol and methyl formate condensate leave cooler/condenser 30 by line39, and are recycled through pump 34 to reactor 12.

In a specific embodiment of the method of this invention, blast furnacegas comprising in mole percent, 55 percent nitrogen, 40 percent carbonmonoxide, 4.5 percent hydrogen and 0.5 percent methane, with water andcarbon dioxide removed, was compressed to 2600 psig and reacted withmethanol and sodium methoxide in the ratio of 1 part by weight sodiummethoxide per 100 parts methanol as described supra. The solutionproduct of the reaction analyzed, on a mole per cent basis, as follows:

methyl formate67 methanol-25 sodium methoxide-1.0

carbon monoxide5.0 (dissolved) nitrogen-2.0

hydrogennegligible methane-negligible The product solution from abovewas degassed by first lowering the temperature to 20 C followed bylowering the pressure to about 300 psig. The product solution thenanalyzed, on a mole per cent basis,

' methyl formate-70.5

methanol-26.3

sodium methoxidel .0

carbon monoxide-2.0 (dissolved) nitrogen-about 0.1 to 02 Heating theproduct solution to 55 C. and removing the gaseous product whilemaintaining solution pressure at 300 psig gave a regenerated gas streamwhich was then cooled to 15-18 C. 0n analysis the gaseous product wasfound to contain, in mole per cent:

carbon monoxidemethyl formate-4.5

nitrogen-0.5 Further cooling of the gaseous product reduced the methylformate content, producing a final product gas stream which analyzed99.5 percent carbon monoxide.

An alternate embodiment of the process of this inabout 300 C. causingcarbon monoxide to regenerate at a pressure above 2500 psig. V

Gaseous products from carbon monoxide generator 44 entercooler/condenser 46 by line 45 where the regenerated carbon monoxide ispurified by condensing methanol and methyl formate from the vapors.Product carbon monoxide emerges from cooler/condenser 46 at line 48while liquid methanol and methyl formate leave cooler/condenser 46 byline 50, and are further cooled in cooler 52 and returned to reactor 12by pump 54.

Our process is equally applicable to other lower alcohols and theircorresponding alkali metal alkoxides, such as for example, ethanol andalkali metal ethoxide, normal and isopropanol, and alkali metalpropoxide, the butanols and alkali metal butoxides.

We claim:

1. A process for recovering carbon monoxide from a fuel gas comprisingthe steps of:

a. compressing a fuel gas containing carbon monoxide at a pressure ofabout 2500 psig. to about 5000 psig.,

b. reacting the compressed fuel gas with a lower alkyl .alcohol in thepresence of an alkali metal alkoxide to form an alkyl formate at fromabout 60 C. to about 100 C.,

c. separating the alkyl formate from the compressed fuel gas, and

d. decomposing the alkyl formate in the presence of the alkali metalalkoxide at a temperature of about 35 C. to about 200 C. whilemaintaining thepressure below about 2500 psig. to form lower alkylalcoho] and liberate carbon monoxide therefrom.

2. A process according to claim 1 in which the fuel gas is blast furnacegas.

3. A process according to claim 1 in which the lower alkyl alcohol ofstep (b) is methanol and the alkali metal alkoxide of step (b) is sodiummethoxide.

4. A process according to claim 3 in which the separating step (c)includes cooling the alkyl formate to a temperature of about 15 C. toabout 20 C. and

venting the compressed fuel gas.

5. The process according to claim 1 further comprising the steps of:

e. recovering the lower alkyl alcohol formed in step (d) and recyclingthe lower alkyl alcohol to step (b), and

f. condensing the lower alkyl alcohol and alkyl formate vapors from step(d) and recycling the lower alkyl alcohol to step (b) and the alkylformate to step (d).

6. The process according to claim 5 in which the fuel gas is blastfurnace Sgps, the fuel gas in step (a? is compressed to about 2 0 psig,the ower alkyl a cohol of step (b) is methanol and the alkali metalalkoxide of step (b) is sodium methoxide, the reacting step (b) isperformed in a temperature range of about to 100 C., the separating ofstep (c) includes cooling the alkyl formate to a temperature of about 20C. and venting the compressed gas at a pressure of less than about 2500psig., and the decomposing of step(d) includes heating the alkyl formatein a chamber to a temperature of about 55 C. at a pressure no greaterthan about 2500 psig.

1. A process for recovering carbon monoxide from a fuel gas comprisingthe steps of: a. compressing a fuel gas containing carbon monoxide at apressure of about 2500 psig. to about 5000 psig., b. reacting thecompressed fuel gas with a lower alkyl alcohol in the presence of analkali metal alkoxide to form an alkyl formate at from about 60* C. toabout 100* C., c. separating the alkyl formate from the compressed fuelgas, and d. decomposing the alkyl formate in the presence of the alkalimetal alkoxide at a temperature of about 35* C. to about 200* C. whilemaintaining the pressure below about 2500 psig. to form lower alkylalcohol and liberate carbon monoxide therefrom.
 2. A process accordingto claim 1 in which the fuel gas is blast furnace gas.
 3. A processaccording to claim 1 in which the lower alkyl alcohol of step (b) ismethanol and the alkali metal alkoxide of step (b) is sodium methoxide.4. A process according to claim 3 in which the separating step (c)includes cooling the alkyl formate to a temperature of about 15* C. toabout 20* C. and venting the compressed fuel gas.
 5. The processaccording to claim 1 further comprising the steps of: e. recovering thelower alkyl alcohol formed in step (d) and recycling the lower alkylalcohol to step (b), and f. condensing the lower alkyl alcohol and alkylformate vapors from step (d) and recycling the lower alkyl alcohol tostep (b) and the alkyl formate to step (d).